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I I I I I I I I I I I I I I I I I I I 3696 PARADOX VALLEY UNIT - COLORADO Paradox Valley is located in Montrose County in southwestern Colorado and is approximately 24 miles long and from 1 to 3 miles wide. The Dolores River crosses this valley near its midpoint about 4 miles upstream from its confluence with the San Miguel River. : The climate of this area is generally semiarid with hot and dry summers and cold and dry winters. Economic activity in this area consists of about 3,600 acres of irrigated cropland in the northwestern half of the valley along with livestock grazing, oil exploration, mining and some lumber ing production. Paradox Valley is one of five major collapsed salt inclines (elongated swells) in southwestern Colorado and southeastern Utah. The erosion of faulted and uplifted sandstone and shale formations has exposed a residual gypsum cap which covers about 15,000 feet of nearly pure salt and salt-rich shale. Groundwater comes into contact with the top of this salt formation and eventually surfaces as salt brine in the channel of the Dolores River near the middle of the valley. The effect of this brine varies considerably with the amount of flow in the river. High flows dilute its effect, but low flows have had salt concentrations as high as 166,000 mg/L which is approximately 5 times as saline as sea water. The current plan and initial test studies indicate that wells could be drilled into the brine on both sides of the river to pump the saline groundwater. This pumping would then lower the inter- fare between the relatively fresh water and the extremely saline brine. It was initially thought that it would require a pumping rate of 5.0 cubic feet per second (cfs) to effectively lower this interfare, but recent studies indicate a rate of 1.5 to 2.0 cfs may accomplish the same objective. These wells and appurtenant disposal facilities would be designed to remove an average of 180,000 tons of salt per year which translates to a decrease of 18 mg/L of salt concentration at Imperial Dam. There are currently two alternative disposal methods being investigated: deep well injection and an evaporation pond. The estimated annual cost based on July, 1981, prices for the evaporative pond alternative is $301,000 per mg/L. The construction of the project with the evaporative pond was esti- mated in early 1980 to be finished by the end of 1986. The draft report on "Deep Well Injection of Brine--Paradox Valley Unit" prepared by Williams Brothers Engineering Company for BuRec has estimated the annual cost for this disposal method to be between $100,000 per mg/L and $250,000 per mg/L depending on the number of injection wells required. Various information is currently being prepared in order to file for an Underground Injection Control Permit with the State of Colorado and the EPA. (Updated 11/20/81) DS:cs -29-